Preparation of tetraalkyllead



Patented Dec. 26, 1 950 PREPARATION OF TETRAALKYLLEAD Hymin Shapiro, Detroit, Mich., assignor to Ethyl Corporation, New of Delaware York, N. Y., a corporation No Drawing. Application May 29, 1948,

, Serial No. 30,193

6 Claims. (01. 260-437) This invention relates to the manufacture of tetraalkyllead. More particularly, it relates to a process for reacting a magnesium-lead alloy with either an alkyl bromide or an alkyl iodide to form a tetraalkyllead. The manufacture of tetraethyllead is of considerable importance because of its use as an antiknock agent in motor fuels. It is used in most of the gasolines presently marketed. Therefore, the economics of its manufacture is also of major importance.

The present commercial process for the manufacture of tetraethyllead has been used for a number of years, and, in general, is satisfactory. However, ithas certain disadvantages which are overcome b practicing my invention. The present commercial process is expressed by the following chemical equation:

In the process as illustrated in the above equation, if the composition of the alloy is controlled to correspond substantially to NaPb, the reaction goes readily to completion without a catalyst and tetraethyllead yields of about 21 per cent by weight based on the lead input are obtained.

It is to be noted, however, that in the NaPb reaction, about three-quarters of the original lead present is converted to finely divided metal considerably contaminated with the product. The presence of this large amount of unused lead in the autoclaves makes temperature control difficult, results in a low overall rate of product output, and necessitates a relatively large investment in equipment. Furthermore, the conversion of the finely divided lead to a form suitable for use in making the NaPb alloy is a hazardous and expensive operation.

It is an object of this invention to provide a process for making tetraalkyllead overcoming the above objections, particularly in making more efiicient use of the lead. This is accomplished in my invention by m discovery that tetraalkyllead compounds can be made by reacting either an alkyl bromide or an alkyl iodide with a magnesium-lead alloy as illustrated by the following chemical equation:

It is to be noted that in the above equation, no lead in the alloy is converted to metallic lead as contrasted with over 75 per cent of lead converted from the alloy to finely divided metal in the present commercial operation.

Various alkyl iodides and bromides can be used to react with the MgzPb alloy to form the corresponding tetraalkyllead compounds, such as the iodides of methane, ethane, propane, and butane, as well as the corresponding bromides.

My process can be carried out at temperatures from room temperature up to 150 degrees centigrade although the preferred range is from to 120 degrees centigrade. Pressures from a few pounds above atmospheric to four hundred pounds per square inch can be employed advantageously. Best yields are obtained by using an alloy corresponding to MgzPb (19.01 per cent Mg by weight), but good yields are obtainable with a magnesium content varying from 18 to 22 per cent by weight. As the magnesium content varies outside of this range, the alloy becomes progressively more difiicult to crush and inferior results are obtained. I

The time for the reaction can also be varied over a wide range. In closed bomb operations, the reaction time has been varied between two and sixteen hours with good results.

My invention is further illustrated by the following example: 10 grams of MgzPb alloy and 34 grams of ethyl bromide were introduced into a tumbled bomb. The alloy, comprising about 19 per cent by weight Mg, was first ground in a chipmunk crusher to a particular size, varying from four to mesh, substantially threequarters of the ground alloy being in the range of from four to 40 mesh. The bomb was then closed off and tumbled for four hours at degrees centigrade. The maximum pressure reached was 113 pounds per square inch. The reaction is exothermic and cooling must be employed after reaction is under way in order to maintain the desired temperature. In this experiment, the temperature was controlled by controlling the temperature of the bath in which the bomb was immersed. In commercial practice, cooling water, suitably applied, can be used. At the end of four hours, the bomb is cooled and the product analyzed for tetraethyllead. Again, in commercial operations the product can be distilled in vacuum or in the presence of steam to recover the tetraalkyllead product. In this example, an analysis showed that 2.41 grams of tetraethyllead were produced, which is equivalent to 19.1 per cent by weight based on the lead input.

In a second experiment, using the same quantity of the same charging materials, but maintaining the bomb at 100 degrees centigrade for 16 hours, 2.98 grams of tetraethyllead were produced, which is equivalent to 23.6 per cent by weight based on the lead input.

In a third experiment, the same quantity of alloy was used, but 45 grams of methyl iodide were introduced into the bomb and the bomb tumbled for 16 hours at 60 degrees centigrade, with a resulting pressure of pounds per square inch. This experiment yielded 1.26 grams of tetramethyllead, which is equivalent to 10 per cent by weight based on the lead input.

v 'In a fourth experiment, similarly conducted, lfO grams of the lead alloy and 49 grams of ethyl iodide were introduced into the bomb, which was tumbled for two (2) hours at 120 degrees centigrade, the pressure being 40 pounds per square inch. In this experiment 1.92 grams of tetraethyllead were produced, which is equivalent to 15.2 per cent by weight based on the lead input.

In all cases, an excess of alkyl halide over the theoretical amount required is preferred. Not only does an excess increase the yield, but also it increases the rate of production which is important in commercial operation because it 'reduces equipment size and cost. Also, an excess of halide maintains a liquid which provides for better heat transfer in maintaining, by cooling, the desired temperature of operation.

The examples given herein are illustrative of my invention, but do not limit the scope thereof. The reaction can be carried out in commercial retorts, or in continuous coil operations. The

,manner of operation, as well as the equipment used can be considerably varied within the .scope of my invention.

I claim:

1. A non-catalytic process for making tetraalkyllead comprising reacting an alloy consisting of lead and magnesium with a lower alkyl'halide g Number sisting of alkyl iodides and alkyl bromides.

3. A process for making tetraethyllead comprising reacting an alloy consisting of about 19 per cent by weight magnesium and about 81 per cent by weight lead with a lower alkyl halide selected from the group consisting of ethyl iodide and ethyl bromide.

4. The process of claim 3 wherein the temperature is maintained between about and 150 C. during the course of the reaction.

5. A process for making tetraethyllead comprising reacting an alloy consisting of about 19 per cent by weight magnesium and about 81 per cent by weight lead with ethyl iodide at a temperature within the range of to C.

6. A process for making tetraethyllead comprising reacting an alloy consisting of about 19 per cent by weight magnesium and about 81 per cent by weight lead with ethyl bromide at a temperature within the range of 60 -to 120 C.

HYMIN SHAPIRO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 2,000,069 Downing et ,al. May 7, 1935 

1. A NON-CATALYTIC PROCESS FOR MAKING TETRAALKYLLEAD CONPRISING REACTING AN ALLOY CONSISTING OF LEAD AND MAGNESIUM WITH A LOWER ALKYL HALIDE SELECTED FROM THE GROUP CONSISTING OF ALKYL IODIDES AND ALKYL BROMIDES. 